The present invention relates generally to nonimpact printing heads, and in particular to an ink jet printing head having a plurality of nozzles in which the combined effects of air pressure gradient and electric potential gradient are utilized to discharge a controlled number of jet streams of ink droplets.
The ink jet printing head shown and described in Japanese Patent Application 56-8428 filed Jan. 1, 1981 comprises an airflow chamber having a single air-liquid nozzle through which a combined stream of air and ink droplets is discharged toward a writing surface. The airflow chamber is connected to a pressurized air supply source for causing an airstream to make a sharp turn at the entry into the air-liquid nozzle, creating a sharp pressure gradient in the liquid discharge path. A liquid nozzle, connected to an ink supply, is axially aligned with the air-liquid nozzle. By the action of the pressure gradient the meniscus of ink at the liquid nozzle is convexed toward the air-liquid nozzle. An electrode is provided for establishing an electric field between the air-liquid nozzle and the convexed meniscus of the liquid to cause it to extend toward the air-liquid nozzle by electrostic attraction and to be torn apart into a droplet which is carried by the airstream and discharged through the air-liquid nozzle.
To make the operating speed of the nonimpact printer consistent with the high-speed data handling capability of the apparatus with which it is to be associated, it is desired that the printing head have a row of plural nozzles to enable simultaneous printing of dots. One approach would be to provide a plurality of liquid nozzles. For proper operation of the printer head the liquid nozzle must be aligned with one-to-one correspondence with the air-liquid nozzles with a high degree of precision. Because of close tolerances this alignment is extremely difficult to achieve.